Project Summary-Abstract The evolution and ontogeny of lifespan at the species and individual level, the energetics of the organism in its environment, the storage of metabolizable energy as body fat, and socioeconomic disparities within populations all seem intricately related and yet the nature of these interrelations is poorly understood. Indeed questions as fundamental as why we age remain open and subsidiary questions such as why caloric restriction leads to increased lifespan and why lower socioeconomic status is related to obesity in developed countries also remain unanswered. Herein, we propose a unified model informed by evolutionary thinking about life strategies which connects these phenomena. In this model, aging or more precisely senescence is not something that passively happens to us as the result of environmental insults or from metabolizing fuel, but is something we do. That is, mortality rate or the rate of aging is seen as (partially) internally regulable phenomenon much like the control of body temperature in homeotherms in which the regulated rate is responsive to perceptions about the energetic state of the environment. From this perspective, it is perceptions of the energetic security of the environment that are a key factor in linking these phenomena. We elaborate this theory herein and from it derive seven specific hypotheses, each of which is testable in a different experiment using model organisms. We have assembled a team of the world's leading researchers to conduct these seven experiments and then to conduct follow-up work to study both a priori specified potential causal mechanisms involving internal clock regulation and also to conduct exploratory work to identify new potential mechanisms. Outcomes from this work will have profound implications for our understanding of the nature of aging, of health disparities, and of obesity.